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Merge patch series "two nits for path lookup"

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Mateusz Guzik <mjguzik@gmail.com> says:

Since path looku is being looked at, two extra nits from me:

1. some trivial jump avoidance in inode_permission()

2. but more importantly avoiding a memory access which is most likely a
cache miss when descending into devcgroup_inode_permission()

the file seems to have no maintainer fwiw

anyhow I'm confident the way forward is to add IOP_FAST_MAY_EXEC (or
similar) to elide inode_permission() in the common case to begin with.
There are quite a few branches which straight up don't need execute.
On top of that btrfs has a permission hook only to check for MAY_WRITE,
which in case of path lookup is not set. With the above flag the call
will be avoided.

* patches from https://lore.kernel.org/20250416221626.2710239-1-mjguzik@gmail.com:
  device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()
  fs: touch up predicts in inode_permission()

Link: https://lore.kernel.org/20250416221626.2710239-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-04-17 11:03:52 +02:00
commit c4044870ae
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GPG key ID: 91C61BC06578DCA2
2 changed files with 9 additions and 8 deletions
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10
fs/namei.c
View file

@ -571,14 +571,14 @@ int inode_permission(struct mnt_idmap *idmap,
int retval;
retval = sb_permission(inode->i_sb, inode, mask);
if (retval)
if (unlikely(retval))
return retval;
if (unlikely(mask & MAY_WRITE)) {
/*
* Nobody gets write access to an immutable file.
*/
if (IS_IMMUTABLE(inode))
if (unlikely(IS_IMMUTABLE(inode)))
return -EPERM;
/*
@ -586,16 +586,16 @@ int inode_permission(struct mnt_idmap *idmap,
* written back improperly if their true value is unknown
* to the vfs.
*/
if (HAS_UNMAPPED_ID(idmap, inode))
if (unlikely(HAS_UNMAPPED_ID(idmap, inode)))
return -EACCES;
}
retval = do_inode_permission(idmap, inode, mask);
if (retval)
if (unlikely(retval))
return retval;
retval = devcgroup_inode_permission(inode, mask);
if (retval)
if (unlikely(retval))
return retval;
return security_inode_permission(inode, mask);

7
include/linux/device_cgroup.h
View file

@ -18,15 +18,16 @@ static inline int devcgroup_inode_permission(struct inode *inode, int mask)
{
short type, access = 0;
if (likely(!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)))
return 0;
if (likely(!inode->i_rdev))
return 0;
if (S_ISBLK(inode->i_mode))
type = DEVCG_DEV_BLOCK;
else if (S_ISCHR(inode->i_mode))
else /* S_ISCHR by the test above */
type = DEVCG_DEV_CHAR;
else
return 0;
if (mask & MAY_WRITE)
access |= DEVCG_ACC_WRITE;